1. Field of the Invention
The present invention relates generally to a gas flushing apparatus for a metallurgical vessel, and more particularly to a gas flushing apparatus having a gas permeable portion which is adapted for connection to a gas supply and which extends from a bottom end to a top end of the gas flushing apparatus.
2. Description of the Prior Art
Gas flushing apparatus, such as capillary gas flushing apparatus and labyrinth gas flushing apparatus, have been known in the art. Such gas flushing apparatus generally include a gas-permeable portion which is adapted for connection to a single gas line. The gas-permeable portion must have a cross sectional dimension engineered to allow a volume of gas which is to pass therethrough to be forced into the metallurgical vessel (i.e. into the molten metal contained in the metallurgical vessel) at a speed which is adequate for proper flushing. It is necessary to vary the rate (i.e. volume per unit time) at which gas is injected into the molten metal to provide for various types of flushing. For example, when a "fine flushing" is desired, the gas flow rate must be reduced. With such conventional gas flushing apparatus, the reduction in gas flow rate results in a reduction of the speed at which the gas is injected into the molten metal. Such reduction in the speed of gas injection into the molten metal deleteriously effects the mixing of the flushing gas with the molten metal.
A gas flushing apparatus has been disclosed in EP 0 221 250 Al which is designed to provide an increased gas flow velocity so as to compensate for a reduction in gas flow velocity due to frictional resistance and the like as the gas flows through the gas flushing apparatus. This increase in gas flow velocity is accomplished by shaping the gas passage of the gas flushing apparatus in the shape of a nozzle. However, this design does not overcome the above-noted disadvantage of a reduction in the speed of gas flow upon reducing the rate of gas flow through the gas flushing apparatus.